In recent years, a substantial improvement of the properties of elements configuring the electronic devices and the starting materials for manufacturing the electronic devices has been strongly demanded with a reduction in size, an enhancement of performance, and a reduction in weight of various electronic devices.
For example, a multilayer ceramic capacitor (MLCC) has been increasingly strongly demanded to reduce the layer thickness. Therefore, barium titanate for use in dielectric layers in the MLCC has been increasingly demanded to be uniform fine particles and to be high in tetragonality and to be superior in dispersibility, for example.
Heretofore, as a method for producing barium titanate, a solid phase method, an oxalic acid method, a sol-gel method, and the like are known. However, in order to produce barium titanate fine particles, particularly those having a particle diameter of about 250 nm or less, preferably about 150 nm or less, for satisfying the recent demand for the reduction in layer thickness of the MLCC, a hydrothermal process which is a wet process is advantageous. Since the solid phase method and the oxalic acid method include a calcination process, uniform particles are difficult to obtain, and moreover the resulting particles are easy to aggregate so that fine particles are difficult to obtain. The sol-gel method employs an expensive alkoxide as the raw material, and therefore the sol-gel method has a problem in the production cost.
Various methods for producing barium titanate by the hydrothermal process are heretofore already known. By way of example, a method is mentioned in which an aqueous solution of barium salt is added to and reacted with a slurry of hydrous titanium oxide in the presence of a carboxylic acid to produce barium titanate core particles, the slurry containing the barium titanate core particles thus obtained is subjected to hydrothermal treatment to obtain spherical barium titanate particles, and then the obtained spherical barium titanate particles are calcined at a temperature of 800° C. to 1200° C. (Patent Literature 1).
According to this method, barium titanate fine particles having a relatively large BET specific surface area and a high tetragonality can be obtained. However, as the method requires calcination of barium titanate core particles, it is difficult to obtain particles having a uniform particle diameter. It is also difficult to obtain particles of fine particles because of aggregation of particles. The use of such barium titanate as a dielectric material in the manufacturing of MLCC poses difficulty in satisfying the demand of reducing the layer thickness of MLCC.